1. Field of the Invention
The present invention relates a method of, and an apparatus for highly precisely performing a positive displacement extrusion of a viscous material, such as unvulcanized rubber.
2. Description of Related Art
A positive displacement pump is widely used for discharging a constant volume of various kinds of fluid. Typically, a positive displacement pump includes a cylinder device comprised of a piston and a cylinder, a shoe plate for causing a reciprocating movement of the piston in the cylinder, and a valve mechanism driven synchronously with the shoe plate such that a constant volume of fluid is introduced into, and discharged from the cylinder during a stroke motion of the piston. This type of positive displacement pump is known to be an effective means for discharging a constant volume of fluids. With such a pump, it is readily possible to adjust the discharge volume of the fluid by changing the stoke of the piston, and also to eliminate fluctuation or pulsation in the discharge volume by increasing the number of the cylinder device.
However, particularly when used to extrude a highly viscous material, such as unvulcanized rubber, the above-mentioned positive displacement pump often suffers from clogging of the viscous material between the opposite surfaces of the piston and the cylinder. In this instance, the viscous material tends to be forced by the shoe plate to cause damages of the cylinder device. Moreover, the inlet and the outlet of the cylinder are of a round shape, and such a shape is considered to be a major cause of unsatisfactory positive displacement performance of the pump.
It is therefore a primary object of the present invention to realize an improved positive displacement extruder for a viscous material, which is substantially free from the problem of clogging of the viscous material and which provides a satisfactory positive displacement performance.
According to a first aspect of the present invention, there is provided a positive displacement extruder for a viscous material, comprising: a main body having a chamber therein and an inlet and an outlet for the viscous material, said inlet and outlet being in communication with the chamber; a feed member rotatably arranged in the chamber of the main body and adapted to be driven for rotation so that the viscous material charged into the chamber through the inlet is extruded from the outlet; a mouthpiece having an inlet that is spaced in a circumferential direction from the outlet of the main body, and an extrusion nozzle in communication with the inlet of the mouthpiece; at least one cylinder device comprising a cylinder and a piston that can be reciprocated in the cylinder, said cylinder device being rotatable about a center axis of the extruder so that the cylinder is alternately bought into communication with the outlet of the main body and the inlet of the mouthpiece; and a cam device for causing a reciprocating movement of the piston in the cylinder.
With the extruder according to the present invention, the viscous material introduced into the chamber of the main body is moved toward the outlet under the rotation of the feed member, and then fully charged into the cylinder of the cylinder device as it is brought into communication with the chamber of the main body. When the cylinder device charged with the viscous material is further rotated so that the cylinder reaches a position where it establishes a communication with the mouthpiece, the advancing stroke movement of the piston induced by the cam device forces the viscous material into the mouthpiece so as to be extruded from the extrusion nozzle, until the cylinder device is moved past the inlet of the mouthpiece.
It is assumed that after the cylinder device has moved past the outlet of the main body, the outlet is tightly sealed by an appropriate seal device that is rotatable with the cylinder device, until the cylinder device reestablishes the communication with the chamber in the main body. Similarly, after the cylinder device has moved past the inlet of the mouthpiece, the inlet is tightly sealed by the seal device until the cylinder device reestablishes the communication with the mouthpiece.
The transfer of the viscous material from the cylinder device to the mouthpiece is steadily carried out during the period in which the cylinder device is in communication with the mouthpiece. When the cylinder device moves past the inlet of the mouthpiece, all the volume of the viscous material in the cylinder has been simultaneously transferred into the mouthpiece without any remainder in the cylinder. As a result, a precisely predetermined volume of the viscous material can be steadily extruded from the nozzle of the mouthpiece, without causing clogging in the interior of the extruder. The extruder according to the present invention can be readily realized to have a compact structure, and is substantially free from noticeable fluctuation or pulsation in the discharge volume of the viscous material.
In a preferred embodiment of the present invention, the extruder comprises a plurality of the cylinder devices that are arranged around the center axis of the extruder as being circumferentially spaced from each other. In this instance, during the period in which the viscous material from the outlet of the main body is charged into the cylinder of one cylinder device, the viscous material contained in the cylinder of another cylinder device can be synchronously discharged into the mouthpiece though the inlet thereof. Thus, while preserving the functional advantage that a highly precise volume of the viscous material can be steadily discharged, it is possible to provide a further improved extrusion efficiency of the extruder.
In another preferred embodiment of the present invention, the extruder further comprises a common drive for the feed member and the cylinder device. In this instance, it is possible to reduce the equipment cost and the running cost of the extruder, and also to realize a compact structure as a whole.
According to a second aspect of the present invention, there is provided a method for extruding a viscous material with the positive displacement extruder explained above, wherein the method comprises the steps of: causing said at least one cylinder device to rotate about the center axis of the extruder; and charging the viscous material from the outlet of the main body into the cylinder, and subsequently discharging the viscous material from the cylinder into the inlet of the mouthpiece, during one turn of rotation of the cylinder device about the center axis of the extruder. In this way, since the cylinder device has a constant volume of the cylinder, a constant volume of the viscous material from the chamber of the main body can be charged into the cylinder of the cylinder device, and also the same constant volume of the viscous material from the cylinder can be charged into the mouthpiece, thereby allowing a positive displacement of the viscous material to be performed highly accurately.
Advantageously, the above-mentioned method according to the present invention is carried out by using an extruder comprised of a plurality of cylinder devices that are arranged about the center axis of the extruder and circumferentially spaced from each other. It is then preferred that the viscous material is charged into the cylinder of one cylinder device and, synchronously therewith, the viscous material is discharged from the cylinder of another cylinder device.
The discharge of the viscous material from the cylinder of one cylinder device is preferably started immediately before completion of the discharge of the viscous material from the cylinder of another cylinder device. In this instance, for example, during a progressive decrease in the opening degree of the cylinder of a first cylinder device with respect to the inlet of the mouthpiece and, hence, in the discharge rate of the viscous material from the first cylinder device, the opening degree of the cylinder of the second cylinder device with respect to the inlet of the mouthpiece is progressively increased to gradually decrease the discharge rate of the viscous material. Thus, fluctuation or pulsation in the discharge rate of the viscous material from the nozzle of the mouthpiece is minimized and the overall discharge rate of the viscous martial is maintained substantially constant.